﻿#pragma once

namespace fast_io::details
{
// clang-format off
/*
Referenced from UTF-EBCDIC
Unicode Technical Report #16
UTF-EBCDIC
EBCDIC-Friendly Unicode (or UCS) Transformation Format
1999-06-24
https://www.unicode.org/reports/tr16/tr16-5.html
*/
inline constexpr char8_t bm_i8_to_ebcdic[256]{
    0x0,  0x1,  0x2,  0x3,  0x37, 0x2D, 0x2E, 0x2F, 0x16, 0x5,  0x15, 0xB,  0xC,  0xD,  0xE,  0xF,  0x10, 0x11, 0x12,
    0x13, 0x3C, 0x3D, 0x32, 0x26, 0x18, 0x19, 0x3F, 0x27, 0x1C, 0x1D, 0x1E, 0x1F, 0x40, 0x5A, 0x7F, 0x7B, 0x5B, 0x6C,
    0x50, 0x7D, 0x4D, 0x5D, 0x5C, 0x4E, 0x6B, 0x60, 0x4B, 0x61, 0xF0, 0xF1, 0xF2, 0xF3, 0xF4, 0xF5, 0xF6, 0xF7, 0xF8,
    0xF9, 0x7A, 0x5E, 0x4C, 0x7E, 0x6E, 0x6F, 0x7C, 0xC1, 0xC2, 0xC3, 0xC4, 0xC5, 0xC6, 0xC7, 0xC8, 0xC9, 0xD1, 0xD2,
    0xD3, 0xD4, 0xD5, 0xD6, 0xD7, 0xD8, 0xD9, 0xE2, 0xE3, 0xE4, 0xE5, 0xE6, 0xE7, 0xE8, 0xE9, 0xAD, 0xE0, 0xBD, 0x5F,
    0x6D, 0x79, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x98,
    0x99, 0xA2, 0xA3, 0xA4, 0xA5, 0xA6, 0xA7, 0xA8, 0xA9, 0xC0, 0x4F, 0xD0, 0xA1, 0x7,  0x20, 0x21, 0x22, 0x23, 0x24,
    0x25, 0x6,  0x17, 0x28, 0x29, 0x2A, 0x2B, 0x2C, 0x9,  0xA,  0x1B, 0x30, 0x31, 0x1A, 0x33, 0x34, 0x35, 0x36, 0x8,
    0x38, 0x39, 0x3A, 0x3B, 0x4,  0x14, 0x3E, 0xFF, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4A, 0x51,
    0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6A, 0x70, 0x71,
    0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x80, 0x8A, 0x8B, 0x8C, 0x8D, 0x8E, 0x8F, 0x90, 0x9A, 0x9B, 0x9C, 0x9D,
    0x9E, 0x9F, 0xA0, 0xAA, 0xAB, 0xAC, 0xAE, 0xAF, 0xB0, 0xB1, 0xB2, 0xB3, 0xB4, 0xB5, 0xB6, 0xB7, 0xB8, 0xB9, 0xBA,
    0xBB, 0xBC, 0xBE, 0xBF, 0xCA, 0xCB, 0xCC, 0xCD, 0xCE, 0xCF, 0xDA, 0xDB, 0xDC, 0xDD, 0xDE, 0xDF, 0xE1, 0xEA, 0xEB,
    0xEC, 0xED, 0xEE, 0xEF, 0xFA, 0xFB, 0xFC, 0xFD, 0xFE};
inline constexpr char8_t bm_ebcdic_to_i8[256]{
    0x0,  0x1,  0x2,  0x3,  0x9C, 0x9,  0x86, 0x7F, 0x97, 0x8D, 0x8E, 0xB,  0xC,  0xD,  0xE,  0xF,  0x10, 0x11, 0x12,
    0x13, 0x9D, 0xA,  0x8,  0x87, 0x18, 0x19, 0x92, 0x8F, 0x1C, 0x1D, 0x1E, 0x1F, 0x80, 0x81, 0x82, 0x83, 0x84, 0x85,
    0x17, 0x1B, 0x88, 0x89, 0x8A, 0x8B, 0x8C, 0x5,  0x6,  0x7,  0x90, 0x91, 0x16, 0x93, 0x94, 0x95, 0x96, 0x4,  0x98,
    0x99, 0x9A, 0x9B, 0x14, 0x15, 0x9E, 0x1A, 0x20, 0xA0, 0xA1, 0xA2, 0xA3, 0xA4, 0xA5, 0xA6, 0xA7, 0xA8, 0xA9, 0x2E,
    0x3C, 0x28, 0x2B, 0x7C, 0x26, 0xAA, 0xAB, 0xAC, 0xAD, 0xAE, 0xAF, 0xB0, 0xB1, 0xB2, 0x21, 0x24, 0x2A, 0x29, 0x3B,
    0x5E, 0x2D, 0x2F, 0xB3, 0xB4, 0xB5, 0xB6, 0xB7, 0xB8, 0xB9, 0xBA, 0xBB, 0x2C, 0x25, 0x5F, 0x3E, 0x3F, 0xBC, 0xBD,
    0xBE, 0xBF, 0xC0, 0xC1, 0xC2, 0xC3, 0xC4, 0x60, 0x3A, 0x23, 0x40, 0x27, 0x3D, 0x22, 0xC5, 0x61, 0x62, 0x63, 0x64,
    0x65, 0x66, 0x67, 0x68, 0x69, 0xC6, 0xC7, 0xC8, 0xC9, 0xCA, 0xCB, 0xCC, 0x6A, 0x6B, 0x6C, 0x6D, 0x6E, 0x6F, 0x70,
    0x71, 0x72, 0xCD, 0xCE, 0xCF, 0xD0, 0xD1, 0xD2, 0xD3, 0x7E, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7A, 0xD4,
    0xD5, 0xD6, 0x5B, 0xD7, 0xD8, 0xD9, 0xDA, 0xDB, 0xDC, 0xDD, 0xDE, 0xDF, 0xE0, 0xE1, 0xE2, 0xE3, 0xE4, 0xE5, 0x5D,
    0xE6, 0xE7, 0x7B, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0xE8, 0xE9, 0xEA, 0xEB, 0xEC, 0xED, 0x7D,
    0x4A, 0x4B, 0x4C, 0x4D, 0x4E, 0x4F, 0x50, 0x51, 0x52, 0xEE, 0xEF, 0xF0, 0xF1, 0xF2, 0xF3, 0x5C, 0xF4, 0x53, 0x54,
    0x55, 0x56, 0x57, 0x58, 0x59, 0x5A, 0xF5, 0xF6, 0xF7, 0xF8, 0xF9, 0xFA, 0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36,
    0x37, 0x38, 0x39, 0xFB, 0xFC, 0xFD, 0xFE, 0xFF, 0x9F};
inline constexpr char8_t utfebcdic_shadow_flags[256]{
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 9, 9, 9, 9, 9, 9, 9, 9, 9,
    9, 1, 1, 1, 1, 1, 1, 9, 9, 9, 9, 9, 9, 9, 9, 9, 1, 1, 1, 1, 1, 1, 1, 1, 9, 9, 9, 9, 9, 9, 9, 9, 9, 1, 1, 1, 1,
    1, 9, 9, 9, 9, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3,
    3, 3, 3, 3, 1, 3, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 3, 3, 3, 3, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 3, 4, 4,
    4, 4, 1, 4, 1, 1, 1, 1, 1, 1, 1, 1, 4, 4, 4, 5, 5, 5, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 5, 6, 6, 7, 7, 0};
// clang-format on

template <::std::integral T>
	requires(sizeof(T) == 1)
inline constexpr ::std::size_t get_utf_ebcdic_invalid_code_units(T *dst) noexcept
{
	*dst = 0xDD;
	dst[1] = 0x73;
	dst[2] = 0x66;
	dst[3] = 0x73;
	return 4;
}

template <::std::integral T>
	requires(sizeof(T) == 1)
inline constexpr ::std::size_t get_utf_ebcdic_code_units(char32_t code, T *dst) noexcept
{
	if (code < 0xA0)
	{
		*dst = static_cast<T>(bm_i8_to_ebcdic[code]);
		return 1;
	}
	else if (code < 0x400)
	{
		*dst = static_cast<T>(bm_i8_to_ebcdic[static_cast<char32_t>(0b11000000) | (code >> 5)]);
		dst[1] = static_cast<T>(
			bm_i8_to_ebcdic[static_cast<char32_t>(0b10100000) | (code & static_cast<char32_t>(0b11111))]);
		return 2;
	}
	else if (code < 0x4000)
	{
		*dst = static_cast<T>(bm_i8_to_ebcdic[static_cast<char32_t>(0b11100000) | (code >> 10)]);
		dst[1] = static_cast<T>(
			bm_i8_to_ebcdic[static_cast<char32_t>(0b10100000) | ((code >> 5) & static_cast<char32_t>(0b11111))]);
		dst[2] = static_cast<T>(
			bm_i8_to_ebcdic[static_cast<char32_t>(0b10100000) | (code & static_cast<char32_t>(0b11111))]);
		return 3;
	}
	else if (code < 0x40000)
	{
		*dst = static_cast<T>(bm_i8_to_ebcdic[static_cast<char32_t>(0b11110000) | (code >> 15)]);
		dst[1] = static_cast<T>(
			bm_i8_to_ebcdic[static_cast<char32_t>(0b10100000) | ((code >> 10) & static_cast<char32_t>(0b11111))]);
		dst[2] = static_cast<T>(
			bm_i8_to_ebcdic[static_cast<char32_t>(0b10100000) | ((code >> 5) & static_cast<char32_t>(0b11111))]);
		dst[3] = static_cast<T>(
			bm_i8_to_ebcdic[static_cast<char32_t>(0b10100000) | (code & static_cast<char32_t>(0b11111))]);
		return 4;
	}
	else if (code < 0x110000)
	{
		*dst = static_cast<T>(bm_i8_to_ebcdic[static_cast<char32_t>(0b11111000) | (code >> 20)]);
		dst[1] = static_cast<T>(
			bm_i8_to_ebcdic[static_cast<char32_t>(0b10100000) | ((code >> 15) & static_cast<char32_t>(0b11111))]);
		dst[2] = static_cast<T>(
			bm_i8_to_ebcdic[static_cast<char32_t>(0b10100000) | ((code >> 10) & static_cast<char32_t>(0b11111))]);
		dst[3] = static_cast<T>(
			bm_i8_to_ebcdic[static_cast<char32_t>(0b10100000) | ((code >> 5) & static_cast<char32_t>(0b11111))]);
		dst[4] = static_cast<T>(
			bm_i8_to_ebcdic[static_cast<char32_t>(0b10100000) | (code & static_cast<char32_t>(0b11111))]);
		return 5;
	}
	return get_utf_ebcdic_invalid_code_units(dst);
}

struct from_ebcdic_result
{
	char32_t code;
	char8_t len;
};

template <::std::integral T>
	requires(sizeof(T) == 1)
inline constexpr from_ebcdic_result utf_ebcdic_advance(T *src_first, ::std::size_t sz) noexcept
{
	char8_t src0(static_cast<char8_t>(*src_first));
	char8_t shadow{utfebcdic_shadow_flags[src0]};
	if (shadow < 2)
	{
		return {static_cast<char32_t>(bm_ebcdic_to_i8[src0]), 1};
	}
	if (shadow == 9)
	{
		return {0xFFFD, 1};
	}
	if (sz < shadow)
	{
		return {0, static_cast<char8_t>(-1)};
	}
	char32_t res{};
	for (char8_t i{1}; i != shadow; ++i)
	{
		char8_t code(bm_ebcdic_to_i8[static_cast<char8_t>(src_first[i])]);
		if ((code >> 5) != 0b101) [[unlikely]]
		{
			return {0xFFFD, i};
		}
		res = (res << 5) | (code & 0b11111);
	}
	char8_t src0i18{bm_ebcdic_to_i8[src0]};
	switch (shadow)
	{
	case 2:
		return {((static_cast<char32_t>(src0i18 & 0b11111)) << 5) | res, 2};
	case 3:
		return {((static_cast<char32_t>(src0i18 & 0b1111)) << 10) | res, 3};
	case 4:
		return {((static_cast<char32_t>(src0i18 & 0b111)) << 15) | res, 4};
	case 5:
		return {((static_cast<char32_t>(src0i18 & 0b1)) << 20) | res, 5};
	default:
		return {0xFFFD, shadow};
	};
}

} // namespace fast_io::details